System for controlling generator for vehicle

ABSTRACT

A control system for a vehicular generator is provided which can be simplified in construction as the entire system to achieve cost reduction by using only a single control terminal that takes in a control signal from outside and by employing the control signal composed of only three kinds of signals. The system includes a generator  2  having an armature coil  202  and a field coil  201 , a battery  4  to be charged by a power generation voltage, and a control circuit  1 A that adjusts the power generation voltage by controlling to turn a field current supplied to the field coil  201  on and off in accordance with a battery voltage. A single control terminal C is provided on the control circuit  1 A, and an external control unit  5  is connected to the control terminal C. The external control unit  5  supplies either one of a ground signal, an open signal and a pull-up signal to the control terminal C as a control signal in accordance with the battery voltage and an operating condition of the vehicle. The control circuit  1 A interrupts the field current to stop power generation in response to the ground signal, adjust the power generation voltage to a first control voltage for normal time in response to the open signal, and adjusts the power generation voltage to a second control voltage higher than the first control voltage in response to the pull-up signal.

TECHNICAL FIELD

The present invention relates to a control system for a vehiculargenerator which is capable of achieving the simplification of a circuitconfiguration and cost reduction in a control apparatus for adjustingthe generation voltage of the generator by using only three kinds ofcontrol signals supplied from external terminals.

BACKGROUND ART

FIG. 5 is a circuit diagram that illustrates a known control system fora vehicular generator.

In FIG. 5, the known control system for a vehicular generator includes acontrol circuit 1 installed on a vehicle for adjusting the voltage ofpower generated, a vehicle-mounted generator 2 having a field coil 201,an armature coil 202 and a rectifier 203, a key switch 3 that is turnedon when the vehicle is driven to operate, and a vehicle-mounted battery4 adapted to be charged by the power generation voltage output from thearmature coil 202 through the rectifier 203.

The control circuit 1 has a voltage detection circuit for detecting theterminal voltage of the battery 4 (hereinafter referred to as “thebattery voltage”), and adjusts the generated voltage to a predeterminedvalue by controlling to turn a field current supplied to the field coil201 on and off in accordance with the battery voltage.

For this purpose, the control circuit 1 includes an output terminal Bhereinafter referred to as “B terminal”) connected to the battery 4, aninput terminal S (hereinafter referred to as “S terminal”) for detectingthe battery voltage, and a power supply input terminal IG (hereinafterreferred to as “IG terminal”) connected to the battery 4 through the keyswitch 3.

In addition, the control circuit 1 includes a power MOSFET 101 connectedto the field coil 201, a blocking (reverse current prevention) diode 102connected to an output terminal of the power MOSFET 101, a transistor104 for turning the power MOSFET 101 on and off, resistors 103, 105connected to the IG terminal, a comparator 106 for turning thetransistor 104 on and off, a resistor 107 and a variable resistor 108both connected to the S terminal (external voltage detection terminal),and a resistor 109 and a Zener diode 110 connected to the IG terminal.

A junction between the resistors 103, 105 are connected to an outputterminal of the transistor 104 and a gate terminal of the power MOSFET101.

The comparator 106, the resistor 107 and the variable resistor 108together constitute a voltage detection circuit for detecting thebattery voltage.

That is, the resistor 107 and the variable resistor 108 serve to dividethe battery voltage to generate a detection voltage, which is input tothe comparator 106.

A junction between the resistor 107 and the variable resistor 108 isconnected to a comparison input terminal (+) of the comparator 106 whichhas a reference input terminal (−) impressed with a reference voltageVref.

In FIG. 5, when the key switch 3 is turned on (closed) upon starting ofthe vehicle, a gate voltage of the power MOSFET 101 becomes a voltagevalue equal to the battery voltage divided by a voltage division ratioof the resistors 103, 105, whereby the power MOSFET 101 is made into aconductive state. As a result, a field current is supplied to the fieldcoil 201 so that the generator 2 becomes able to generate electricpower.

On the other hand, the Zener diode 110, to which the battery voltage issupplied through the resistor 109, constitutes a constant-voltage powersupply V1 that generates a constant voltage based on the batteryvoltage. Also, a reference voltage Vref (a reference of comparison tothe battery voltage) in the comparator 106 is generated based on theconstant-voltage power supply V1.

When the generator 2 starts generating electricity in accordance withthe engine starting of the vehicle, the voltage detection circuit 107,108 in the control circuit 1 detects the battery voltage from the Sterminal, and inputs it to the comparison input terminal (+) of thecomparator 106.

When this detected voltage becomes higher than the predetermined voltageVref set at the reference input terminal (−), the transistor 104 becomesconductive due to an ON output of the comparator 106, therebyinterrupting or turning off the power MOSFET 101. As a result, the fieldcurrent is decreased to reduce the power generation voltage of thegenerator 2.

On the other hand, when the detected value of the battery voltage fallsbelow the reference voltage Vref, the transistor 104 is interrupted orturned off due to an OFF output of the comparator 106, so that the powerMOSFET 101 becomes conductive. As a result, the field current isincreased to raise the power generation voltage of the generator 2.

Thus, the power generation voltage of the generator 2 is controlled tothe predetermined constant voltage due to the repeated on-off control ofthe field current.

However, when an automotive generator is driven to operate, it becomesnecessary to suppress the power generation voltage in accordance withthe operating condition of the vehicle to reduce the engine load, or onthe contrary to facilitate the power generation voltage so as to rapidlycharge the battery. Therefore, it is necessary to make it possible toset the power generation voltage to three or more kinds of levels.

Accordingly, there has been proposed a system that can change thevoltage adjusted by the control unit in accordance with a control signalfrom an external control unit.

Such a kind of control system for a vehicular generator is described,for example, in Japanese patent application laid-open No. S62-107643. Inthis case, however, there arises a problem that in order to set thepower generation voltage at three levels, two external input terminalsare required, resulting in an increased number of wirings for thecontrol unit.

In addition, Japanese patent No. 3102981, for example, is given as acontrol system in which only a single input terminal from an externalcontrol unit is provided for arbitrarily adjusting a control voltage. Inthis case, however, it is necessary to arrange a circuit for determiningan external input signal inside the control unit, so the construction ofthe control unit becomes very complicated. As a result, there is aproblem that an increase in costs can not be avoided.

DISCLOSURE OF THE INVENTION

The present invention is intended to obviate the problems as referred toabove, and has for its object to obtain a control system for a vehiculargenerator which requires a single control terminal that is dedicated totake in a control signal from the outside, thereby to simplify theentire system and achieve cost reduction, and in which the controlsignal comprises three kinds of signals (a ground signal, an open signaland a pull-up signal).

A control system for a vehicular generator according to the presentinvention includes: a generator that is installed on a vehicle and hasan armature coil and a field coil; a battery that is installed on thevehicle so as to be charged by a power generation voltage output fromthe armature coil; and a control unit that has a voltage detectioncircuit for detecting a terminal voltage of the battery, and adjusts thepower generation voltage to a predetermined voltage by controlling toturn a field current supplied to the field coil on and off in accordancewith the terminal voltage of the battery. A single control terminal isprovided on the control unit. An external control unit is connected tothe control terminal. The external control unit supplies either one of aground signal, an open signal and a pull-up signal to the controlterminal as a control signal in accordance with the terminal voltage ofthe battery and an operating condition of the vehicle. The control unitserves to make the generator into a power generation stop state byinterrupting the field current in response to the ground signal suppliedto the control terminal, adjust the power generation voltage to a firstcontrol voltage for normal time by controlling to turn the field currenton and off in response to the open signal supplied to the controlterminal, and adjust the power generation voltage to a second controlvoltage higher than the first control voltage by controlling to turn thefield current on and off in response to the pull-up signal supplied tothe control terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a control system for a vehiculargenerator according to a first embodiment of the present invention.

FIG. 2 is an explanatory view illustrating one example of a switchingoperation between a first and a second control voltage in accordancewith a control signal according to the first embodiment of the presentinvention.

FIG. 3 is an explanatory view illustrating one example of a gradualincrease (gradual decrease) switching control operation between a firstand a second control voltage based on the duty control of an externalcontrol unit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a control system for a vehiculargenerator according to the second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a known control system for avehicular generator.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1

FIG. 1 is a block diagram that shows a control system for a vehiculargenerator according to a first embodiment of the present invention. InFIG. 1, the parts or components same as those described above (see FIG.5) are identified by the same symbols or by the same symbols with “A”affixed to their ends, while omitting a detailed explanation thereof.

Here, note that to avoid the complexity of the drawings, a resistor 109and a Zener diode 110 that together constitute a power supply circuit ina control circuit 1A are omitted.

In this case, an external control unit 5 is provided in addition to theconstruction as stated above.

In addition, the control circuit 1A is provided with a single controlterminal C (hereinafter referred to as “C terminal”), to which anexternal control unit 5 is connected so that a control signal from theexternal control unit 5 is input to the control terminal C.

The external control unit 5 supplies either one of a ground signalground voltage), an open signal and a pull-up signal (high voltage) tothe C terminal as a control signal in accordance with the batteryvoltage and the operating condition of the vehicle.

Moreover, the control circuit 1A serves to make the generator 2 into apower generation stop state by interrupting or cutting off the fieldcurrent in response to the ground signal supplied to the C terminal.Also, the control circuit 1A adjusts the power generation voltage to afirst control voltage for normal time by controlling to turn the fieldcurrent on and off in response to the open signal supplied to the Cterminal, and adjusts the power generation voltage to a second controlvoltage higher than the first control voltage by controlling to turn thefield current on and off in response to the pull-up signal supplied tothe C terminal.

In FIG. 1, the external control unit 5 includes transistors 501, 502connected to the C terminal, and a control unit 503 for controlling toturn the transistors 501, 502 on and off so as to determine the controlsignal (the input status of the C terminal) supplied to the C terminal.

Further, the control circuit 1A includes, in addition to circuitelements 101 through 108 similar to those as described above, resistors111, 112 and 113 that determine a voltage division ratio of a referenceinput terminal (−) of the comparator 106.

The resistors 111 through 113, which together constitute a voltagedetection circuit in the control circuit 1A, generates a referencevoltage Vref from the constant-voltage power supply V1, as previouslystated.

A diode 114 is inserted between the reference input terminal (−) and theC terminal of the comparator 106.

A transistor 115 has an output terminal connected to a junction betweenthe resistors 112, 113, and a base terminal connected to the IG terminalthrough a resistor 116. Also, the transistor 115 has a base terminalconnected to an output terminal of another transistor 117, which has abase terminal connected to the C terminal through a Zener diode 119 anda resistor 118.

The control circuit 1A adjusts the power generation voltage in responseto a control signal supplied from the external control unit 5 to the Cterminal by changing the voltage division ratio of the resistors 111through 113 to change the reference voltage Vref in accordance with thecontrol signal.

The transistors 115, 117 function as a switching element to change thevoltage division ratio of the resistors 111 through 113, and theresistors 116,118 and the Zener diode 119 function as a circuit elementto turn the transistors 115, through 117 on and off.

Next, reference will be made to a concrete control operation accordingto the first embodiment of this present invention as shown in FIG. 1.

In normal operation, the transistor 104 is turned on and off by anON/OFF output of the comparator 106, as stated above, whereby the powerMOSFET 101 is turned on and off to decrease or increase the fieldcurrent, as a consequence of which the power generation voltage of thegenerator 2 is controlled to be constant by repeatedly turning thisfield current on and off.

However, the voltage division ratio of the reference voltage Vref(divided voltage) set at the reference input terminal (−) side in thecomparator 106 in the control circuit 1A is not a fixed or constantvalue that is determined only by the fixed power supply voltage V1, butchanges into three steps in accordance with an input signal from the Cterminal.

First of all, when the control signal input from the C terminal is a“ground signal (ground voltage)”, in other words, when the transistor501 is turned off (interrupted) and the transistor 502 is turned on(made conductive) by the control unit 503 in the external control unit5, the reference input terminal (−) side of the comparator 106 isgrounded through the diode 114.

As a result, the reference voltage Vref becomes 0 V, so the transistor104 always comes into an ON (conductive) state and the power MOSFET 101always comes into an OFF (interrupted or nonconductive) state.Accordingly, the generator 2 comes into a power generation stop state,and the power generation voltage thereof becomes 0 V.

In addition, when the control signal input from the C terminal is a“open signal”, in other words, when both the transistors 501, 502 areturned off (interrupted) by the control unit 503 in the external controlunit 5, the reference voltage Vref does not remain the ground signal. Inthis case, however, by setting the power supply voltage V1 to a valuelower than the breakdown voltage of the Zener diode 119, the referencevoltage Vref becomes lower than the breakdown voltage of the Zener diode119, too.

Accordingly, the Zener diode 119 is turned off (interrupted), and thetransistor 117 is also turned off (interrupted), and the transistor 115becomes conductive. As a result, a reference voltage Vref1 determined bya voltage division ratio between the resistors 111, 112 is impressed onthe reference input terminal (−) side of the comparator 106.

On the other hand, the divided voltage of the S terminal voltage(battery voltage) is impressed on the comparison input terminal (+) sideof the comparator 106, whereby the battery voltage can be detected.

Accordingly, the comparator 106 controls the power generation voltage ofthe generator 2 to be a fixed or constant voltage by repeatedly turningthe power MOSFET 101 on and off through comparison between the dividedvoltage of the battery voltage and the reference voltage Vref1 (thevalue of the power supply voltage V1 divided by the resistors 111, 112).At this time, the power generation voltage controlled based on thereference voltage Vref1 is called a first control voltage.

Next, when the control signal input from the C terminal is a pull-upsignal (high voltage), in other words, when the transistor 501 is turnedon made conductive) and the transistor 502 is turned off (interrupted)by the control unit 503 in the external control unit 5, the C terminalvoltage is substantially raised to the battery voltage.

Accordingly, the Zener diode 119 is turned on (made conductive), and thetransistor 117 is also turned on (made conductive), and the transistor115 is turned off (interrupted).

As a result, a reference voltage Vref2 determined by a voltage divisionratio between the resistor 111 and the series-connected resistors 111,112 is impressed on the reference input terminal (−) side of thecomparator 106.

The reference voltage Vref2 at this time is a divided voltage valuehigher than the above-mentioned reference voltage Vref1, and hence thepower generation voltage (second control voltage) controlled based onthe reference voltage Vref2 becomes a voltage value higher than theabove-mentioned first control voltage. Hereinafter, the power generationvoltage of the generator 2 is controlled to be constant by the secondcontrol voltage, as stated above.

FIG. 2 is an explanatory view that illustrates one example of aswitching operation for the power generation voltage (between the firstand second control voltages) based on the reference voltages Vref1 andVref2, in conjunction with the ON/OFF operation of the transistors 501,502 in the external control unit 5.

In FIG. 2, the axis of abscissa represents the ON/OFF states of thetransistors 501, 502 (control signals), and the axis of ordinaterepresents the S terminal voltage VS. The input signals at the Cterminal correspond to the control signals, and the S terminal voltageVS corresponds to the battery voltage.

Here, note that in the case of the ground signal (ground voltage), thepower generation voltage is set to 0 V, the first control voltage is setto 14 V, and the second control voltage is set to 15 V.

In this manner, the power generation voltage can be controlled at threelevels of 0 V, 14.5 V (first control voltage) and 15.5 V (second controlvoltage) in accordance with the control signal input from the externalcontrol unit 5 through the single C terminal provided on the controlcircuit 1A. Accordingly, the construction of the control circuit 1A doesnot become complicated.

Moreover, the control signal generated in the external control unit 5comprises only three kinds of signals, that is, the ground signal, theopen signal and the pull-up (high) signal, so the construction of thecontrol circuit 1A can be simplified and hence can be easily achievedwithout inviting an increase in costs.

Further, the control circuit 1A, being composed of a circuit withbipolar transistors, is less prone to influences due to noise, etc., andcan perform control operation in a reliable manner.

Here, note that in FIG. 1, the voltage detection circuit in the controlcircuit 1A serves to set, by switching, the reference voltage Vrefsupplied to the reference input terminal (−) of the comparator 106 so asto correspond to the three kinds of control voltages (0 V, 14.5 V, 15.5V) in response to the three kinds of control signals (C terminalvoltages), but it may switchingly set the detected voltage value of thebattery voltage supplied to the comparison input terminal (+) side ofthe comparator 106.

In this case, the voltage detection circuit in the control unit includesvoltage detection resistors that appropriately divide the batteryvoltage so as to convert it into a detection voltage, and the controlunit adjusts the power generation voltage in response to the controlsignal supplied from the external control unit 5 by changing aresistance ratio between the voltage detection resistors in accordancewith the control signal.

It is needless to say that operational effects equivalent to those asstated above can be obtained in this case, too.

Furthermore, although the S terminal voltage VS is detected at thecomparison input terminal (+) side of the comparator 106, the B terminalvoltage can instead be made as the detected voltage while achievingsimilar operational effects.

Embodiment 2

Though no particular reference has been made in the above-mentionedfirst embodiment, engine rotation is liable to become unstable due to arapid change in the field current (exciting current) supplied to thefield coil 201 in the generator 2 at the time when switching is madebetween the respective control voltages (power generation voltages) (seeFIG. 2). Accordingly, to avoid this, it is preferable to switch betweenthe respective control voltages (power generation voltages: S terminalvoltage) through gradual increase (or gradual decrease) control byapplication of duty control.

In addition, in the above-mentioned first embodiment, the comparator 106is installed inside the control circuit 1A, and the divided voltagevalue (reference voltage) at the reference input terminal (−) sidethereof is changed in accordance with the control signal (C terminalvoltage), but a circuit comprising resistors, a Zener diode andtransistors may be used instead of the comparator 106.

FIG. 3 is an explanatory view that illustrates a gradual increase (orgradual decrease) switching operation for each control voltage based onthe duty control according to a second embodiment of the presentinvention.

FIG. 4 is a circuit diagram that illustrates a control system for avehicular generator according to the second embodiment of the presentinvention, wherein there is shown the case where the operation ofswitching the duty ratio of the base voltage of the transistor 501 ortransistor 502 (see FIG. 3) is achieved by using a circuit comprisingresistors, a Zener diode and transistors.

In FIG. 4, the same parts or components as those described above (seeFIG. 1) are identified by the same symbols or by the same symbols with“B” affixed to their ends, while omitting a detailed explanationthereof.

A control circuit 1B is provided with a Zener diode 120 in place of theabove-mentioned comparator 106.

The Zener diode 120 has a cathode side connected to the S terminalthrough a resistor 121, and grounded through resistors 122, 123 and atransistor 124.

The transistor 124 has a base terminal connected to the C terminalthrough a resistor 127, and at the same time connected to the IGterminal through resistors 127, 126.

A junction between the resistors 122, 123 is grounded through atransistor 125, which has a base terminal connected to the C terminalthrough a Zener diode 128, and at the same time connected to the IGterminal through the Zener diode 128 and the resistor 126.

On the other hand, at the time when the control signal is switched inaccordance with an increase or a decrease in the battery voltage and theoperating condition of the vehicle, a control unit 503B in the externalcontrol unit 5B gradually increases or decreases the base voltage of thetransistor 501 or 502 by controlling it as a duty signal, as shown inFIG. 3.

That is, the control unit 503B makes it possible to gradually increaseor decrease the base voltage according to four kinds of duty controls,as indicated by base voltage waveforms (a) through (d) in FIG. 3, inresponse to four kinds of increase or decrease switchings, as indicatedby arrows (a) through (d) in FIG. 3, with respect to three levels (0 V,14.5 V, 15.5 V) of the S terminal voltage VS (control voltage).

As a result, the control circuit 1B switches the change of the controlvoltage in a linear (straight line) manner so as to adjust the powergeneration voltage in response to the C terminal voltage (duty signal)upon switching of the control signal, whereby the operating condition ofthe vehicle can be made stable while avoiding a rapid change in thefield current.

In FIG. 3, arrow (a) indicates gradual increase control from a powergeneration stop state (VS=0 V) to a first control voltage (VS=14.5 V);arrow (b) indicates gradual increase control from the first controlvoltage (VS=14.5 V) to a second control voltage (VS=15.5 V); (c)indicates gradual decrease control from the second control voltage(VS=15.5 V) to the first control voltage (VS=14.5 V); and (d) indicatesgradual decrease control from the first control voltage (VS=14.5 V) tothe power generation stop state (VS=0 V).

With respect to the respective switching operations as indicated byarrows (a) through (d), the base voltages of the transistors 501, 502 inthe external control unit 5B are duty controlled in the followingmanner.

That is, in the base voltage waveform (a) corresponding to arrow (a),the ON duty ratio of the base voltage of the transistor 502 is graduallydecreased to shift the transistor 502 into its OFF state while keepingthe transistor 501 in its OFF state.

Also, in the base voltage waveform (b) corresponding to arrow (b), theON duty ratio of the base voltage of the transistor 501 is graduallyincreased to shift the transistor 501 into its ON state while keepingthe transistor 502 in its OFF state.

In addition, in the base voltage waveform (c) corresponding to arrow(c), the ON duty ratio of the base voltage of the transistor 501 isgradually decreased to shift the transistor 501 into its OFF state whilekeeping the transistor 502 in its OFF state.

Further, in the base voltage waveform (d) corresponding to arrow (d),the ON duty ratio of the base voltage of the transistor 502 is graduallyincreased to shift the transistor 502 into its ON state while keepingthe transistor 501 in its OFF state.

Thus, when the transistor 501 or the transistor 502 is switched from itsconductive state into its interrupted or nonconductive state or viceversa, by duty controlling their base voltage, the voltage divisionratio at the input side of the comparator 106, which is determined bythe input signal from the C terminal, is controlled to graduallydecrease or increase. Accordingly, the gradual increase and decreasecontrol can be done without changing the construction of the controlcircuit 1B.

Moreover, by using a circuit comprising the resistors 121 through 123,126, 127, the Zener diodes 120, 128 and the transistors 124, 125arranged in the control circuit 1B, as shown in FIG. 4, a controlvoltage switching operation similar to what is done by the comparator106 (see FIG. 1) can be achieved without using the comparator 106.

The other operations of the control circuit 1B are similar to those asdescribed above, and the power MOSFET 101 is turned on and off by theON/OFF operation of the transistor 104 thereby to decrease (or increase)the field current, so that the power generation voltage of the generator2 is controlled to be constant by the repeated on-off control on thefield current.

However, in FIG. 4, the control voltage is changed by a change in thedivided voltage value Vs of the S terminal voltage VS that is determinedin accordance with the control signal input from the C terminal withoutthrough the comparator 106 (see FIG. 1).

Next, reference will be made to the specific operation of the controlcircuit 1B for switching the control voltage while referring to FIG. 4.

In FIG. 4, first of all, when the control signal is a “ground signal”,no base current is supplied to the transistors 124, 125, so both of thetransistors 124, 125 are turned off or in their OFF state, and thedivided voltage value Vs of the S terminal voltage VS becomes equal tothe battery voltage itself.

Accordingly, the Zener diode 120 is made conductive so the transistor104 is always turned on or made into its ON state, as a consequence ofwhich the power MOSFET 101 always becomes interrupted or nonconductive,and hence the power generation voltage becomes 0 V.

On the other hand, when the control signal is a “open signal”, the Zenerdiode 128 is interrupted by the divided voltage value of the batteryvoltage due to the resistors 126, 127, so the transistor 125 is alsointerrupted, and the transistor 124 becomes conductive.

It is needless to say that at this time, the divided voltage value ofthe battery voltage due to the resistors 126, 127 is set to a value thatis lower than the breakdown voltage of the Zener diode 128, but equal toor higher than a voltage value enough to make the transistor 124conductive.

As a result, the divided voltage Vs of the S terminal voltage VS isdetermined by a voltage division ratio between the resistance value ofthe resistor 121 and the series resistance value of the resistors 122,123.

Here, when the divided voltage Vs becomes a voltage value larger thanthe sum of a base voltage that makes the transistor 104 conductive andthe breakdown voltage of the Zener diode 120, the transistor 104 isturned on (made conductive).

On the other hand, when the divided voltage Vs is less than the sum ofthe base voltage that makes the transistor 104 conductive and thebreakdown voltage of the Zener diode 120, the transistor 104 is turnedoff (interrupted).

In this manner, the power generation voltage of the generator 2 iscontrolled to be constant due to the repeated one-off control of thefield current. At this time, the control voltage determined by thedivided voltage Vs is called a first control voltage, as stated above.

In addition, when the control signal is a “pull-up signal”, the Cterminal voltage is raised substantially up to the battery voltage, sothe Zener diode 128 becomes conductive, and the transistor 125 alsobecomes conductive, as a result of which the divided voltage Vs isdetermined by the voltage division ratio of the resistors 121, 122. Atthis time, the control voltage determined by the divided voltage Vs iscalled a second control voltage, as stated above.

As described above, with the control signal from the external controlunit 5B being formed into only one system or group, it is possible tocontrol the power generation voltage at three level. Accordingly, theconstruction of the control circuit 1B and the control unit 503B can besimplified as stated above.

In addition, the control voltage upon switching thereof can be graduallyincreased or decreased by duty controlling the base voltage of thetransistor 501 or 502 by means of the control unit 503B in the externalcontrol unit 5B without particularly changing the circuit configurationof the control circuit 1B. As a consequence, it is possible to make theoperating condition of the vehicle stable by avoiding a sudden change inthe target value of the power generation voltage.

Moreover, by gradually increasing or decreasing the power generationvoltage based on the duty control, it is possible to achieve stableengine rotation even when the battery 4 is being charged at fast speedor when the number of revolutions per minute of the engine is low.

Further, by setting the first control voltage to a normal powergeneration voltage, the control circuit 1B can continue the normalcontrol of the power generation voltage even if the C terminal isdisconnected, for instance.

Although the voltage detection circuit (Zener diode 120) in the controlcircuit 1B uses the divided voltage Vs of the S terminal voltage VS asthe detected voltage of the battery voltage, the B terminal voltage caninstead be used.

In this case, the voltage detection terminal (S terminal) can beomitted, thus making it possible to achieve further cost reduction.

1. A control system for a vehicular generator comprising: a generatorthat is installed on a vehicle and has an armature coil and a fieldcoil; a battery that is installed on said vehicle so as to be charged bya power generation voltage output from said armature coil; and a controlcircuit that has a voltage detection circuit for detecting a terminalvoltage of said battery, and adjusts said power generation voltage to apredetermined voltage by controlling to turn a field current supplied tosaid field coil on and off in accordance with the terminal voltage ofsaid battery; wherein a single control terminal is provided on saidcontrol circuit; an external control unit is connected to said controlterminal; said external control unit supplies either one of a groundsignal, an open signal and a pull-up signal to said control terminal asa control signal in accordance with the terminal voltage of said batteryand an operating condition of said vehicle; and said control circuitserves to make said generator into a power generation stop state byinterrupting said field current in response to said ground signalsupplied to said control terminal, adjust said power generation voltageto a first control voltage for normal time by controlling to turn saidfield current on and off in response to said open signal supplied tosaid control terminal, and adjust said power generation voltage to asecond control voltage higher than said first control voltage bycontrolling to turn said field current on and off in response to saidpull-up signal supplied to said control terminal.
 2. The control systemfor a vehicular generator as set forth in claim 1, wherein said voltagedetection circuit has resistors to generate a reference voltage thatbecomes a comparison reference with respect to the terminal voltage ofsaid battery; and said control circuit adjusts said power generationvoltage in response to said control signal supplied from said externalcontrol unit to said control terminal by changing a voltage divisionratio between said resistors to change said reference voltage inaccordance with said control signal.
 3. The control system for avehicular generator as set forth in claim 1, wherein said voltagedetection circuit has voltage detection resistors that divide theterminal voltage of said battery so as to convert it into a detectedvoltage; and said control circuit adjusts said power generation voltagein response to said control signal supplied from said external controlunit by changing a resistance ratio between said voltage detectionresistors in accordance with said control signal.
 4. The electric powersteering control apparatus for a vehicle as set forth in claim 1,wherein said external control unit controls said control signal into aduty signal upon switching of said control signal; and said controlcircuit switches a change in said control voltage of adjusting saidpower generation voltage in a linear manner by said duty signal uponswitching of said control signal.